What you need to know about the 'supermoon' lunar eclipse

HARI SREENIVASAN: Look up in the sky tonight, and you may see a rare supermoon total lunar eclipse. The sun, Earth, and a full moon will be in a straight line, making the moon, in its closing point of orbit, appear much brighter than usual, even red-orange in some places.

This phenomenon hasn't happened in 33 years and won't happen again for another 18.

For some insight, yesterday I spoke with "NewsHour" science correspondent Miles O'Brien.

Well, why is this so significant for people?

MILES O'BRIEN: When the moon turns big, 14 percent bigger, as it does during this — this so-called supermoon — the moon's orbit is not circular — it's elliptical — this is its closest point.

And then on top of that, you get a total eclipse. This is the fourth in a so-called lunar tetrad, which began in April of 2014, four total eclipses in a row. People start thinking things are going crazy.

HARI SREENIVASAN: Well, why — why does it turn red-orange? Or what is that about?

MILES O'BRIEN: Well, you know, when you see an eclipse of the sun, the moon is passing from the sun, and you get that dark disk. It takes a bite out of the sun, as it were.

In this case, the Earth is eclipsing the sun's rays on to the moon. The moon, of course, has no light of its own. It's reflected light. What happens is — think of it — the colors you see at sunset, as the light goes through the atmosphere of Earth, it gets bounced around, separated and retracted, and what ends up shining on to the moon and getting to the moon is the red range of light. And that's why you see that kind of reddish-orange.

Now, if you are a total pro, look at the beginning and the end. This is a little bit like looking for the green flash when you are looking at the sunset. You will see a blue or violet band that will appear there, because, as the sun passes through the ozone layer of Earth, it retracts slightly differently, and you get a blue tone.

So, get some binoculars out at the beginning and the end of the eclipse, and you might catch that blue band.

HARI SREENIVASAN: So, unlike the solar eclipses, this is totally safe to see, right?

MILES O'BRIEN: Yes, it's great.

It's the best viewing, because you don't have to worry about looking straight at the moon. It's all reflected. You don't have to have binoculars. You can just go out and enjoy it. And it's totally in prime time for the East Coast of the U.S. Assuming no cloud cover, you're going to get quite a show.

HARI SREENIVASAN: So, about 10:00 — 10:00 to 11:00 on the East Coast, and then that means, what, about 7:00 on the West Coast.

MILES O'BRIEN: Yes.

By the time the moon rises on the West Coast, it will already be under way. But they will still get a show there. The full prime-time show will be on the East Coast. And it — you know, the whole thing really begins around the 8:00 p.m. hour, all the way into midnight.

But the actual peak of it will be 10:00 p.m. Eastern time on the East Coast. And it's — it's worth a look. And if you happen to be in an area where it's cloudy — and these things happen — there's about three or four places online where you can see streaming Webcasts. NASA TV is doing it, Sky and Telescope. Slooh is doing it.

So, you will be able to see it one way or another.

HARI SREENIVASAN: But what is it about this that fascinates us? I mean, this is — people have been fascinated by eclipses for as long as history has been written: Oh my God, something stopped the moon, or something changed the color of the sun. What happened?

MILES O'BRIEN: Yes.

I mean, we — science has filled in a lot of blanks for us in recent years. We know that this is simply an alignment of planets. And when the orbits line up in a certain way, the sun, the Earth and the moon line up just perfectly, you get this.

And that makes it all sound kind of clinical, but, before we knew a lot about this, these were looked at as omens. Eclipses in particular have always been looked at as some indication that something usually bad is going to happen.

So, I think we know, scientifically, that isn't necessarily the case. But there are still people out there who worry.

HARI SREENIVASAN: All right.

Miles O'Brien, science correspondent for the "PBS NewsHour," thanks so much for joining us.

MILES O'BRIEN: You're welcome, Hari.